Method of producing sintered alloys of beryllium



Oct.:31, 1967 o ANG ET AL 3,350,201

Original Filed Sept. 11, 1964 INVENTORS HOH Yl ANG ARL R. HELDERMAN wv l A. 181

ATTORNEY United States l atent H 50, 1 METHOD OF PRODUCING SINTERED ALLOYS F BERYLLIUM Choh-Yi Aug, Santa Ana, and Earl R. Helderman, Garden Grove, Calif., assign'ors to North American Aviation, Inc.

Original application Sept. 1-1, 1964, Ser. No. 395,860, now Patent No. 3,325,257, dated June 13, 1967. Divided and this application Jan. 10, 1967, Ser. No.623,i61

8 Claims. '(Cl. 75-214) ABSTRACT OF THE DISCLOSURE A method is described for preparing sintered alloys of beryllium. These alloys, which are substantially isotropic, also may contain copper and aluminum, and exhibit a density of at least '95 percent of the'theoretical maximum density of the alloy composition.

This :is a division of application, Ser. No. 395,860, filed Sept. 11, 1964, now Patent No. 3,325,257. This invention relates to a method for preparing sintered alloys comprising'beryllium, copper, and aluminum.

Beryllium is distinctive in being light in weight, strong and hard, and in having a relatively high melting point.

It has been used, for example, in a copper-beryllium I alloy 'for high electrical conductivity springs, and in pure at least one ingredient beingin the liquid phase, and with at least that ingredient of non-cubic crystal structure being 'in powder form whereby its crystals or grains in the sintered alloy mass are in random orientation.

Attempts have been madeheretofore to produce beryllium alloys by sintering beryllium powder in the presence of liquid phase but these failed to achieve that extent of densification of thealloy which is generally considered in the art of powder metallurgy to be a required minimum in "-order to realize optimum properties, i.e., the sintered alloy should have a density of at least 95 percent of the theoretical maximum density of the alloy composition. Also, the improper selection of ingredients and improper techniques have resulted in the bleeding out of the liquid phase during sintering.

It is another object of this invention to provide beryllium alloys which are not only substantially isotropic but also have a density of at least 95 percent of the theoretical maximum density of the alloy composition. It is contemplated by this invention to provide substantially isotropic beryllium alloys which vary in composition not only in beryllium content but also in the number of ingredients and in concentration ratios thereof so as to provide wide ranges of properties for various uses. In some instances of use, the properties of high thermal and high electrical conductivities may be of primary concern while strength requirements may not be stringent. For other "'uses, the ratioof high modulus to weight may be of pri- Patented Oct. 31, 1967 mary importance while electrical and thermal properties are of secondary consideration. In still other cases, nuclear properties may be important while strength and electrical conductivity, for example, may be of little significance. Then, again, resistance to corrosion may be the primary characteristic for determing the concentrations andnature of ingredients for alloys within the scope of this invention.

Still another object is to provide isotropic beryllium alloys of at least 95 percent densificati'on and which have a high ratio of modulus to weight and are preferably lighter in weight than aluminum.

According to this invention, substantially isotropic beryllium alloys 'are formed by sintering beryllium powder and a mixture comprisingcopper and aluminum, the mixture being in the liquid phase during the sintering operation. The beryllium alloys of this invention are especially well suited for aerospace applications where the attractive physical properties of beryllium prove advantageous. For example, light weight, strong and rigid rotors of beryllium alloys of this invention have been formed for use in inertial instruments, and have been found to be greatly superior to pure beryllium, not only in the desired properties mentioned hereinabove but also in cost of manufacture.

Sintered alloys which consist essentially of copper and beryllium and which are of high beryllium content exhibit anisotropic properties. The melting point of copper being relatively close to that of beryllium, it is difficult to maintain optimum sintering conditions which will'prevent complete alloying and will ensure random orientation of the primary grain structures.

Beryllium and aluminum are substantially immiscible. Aluminum lowers the melting point of copper. Also, the viscosity of molten aluminum-copper alloy is lower than that of molten copper. Thus it is, according to this invention, that beryllium powder may be sintered with mixtures of copper and aluminum at temperatures below the melting point of beryllium, thereby to avoid fusion of beryllium which would cause anisotropy.

The alloys of this invention comprise beryllium, copper, and aluminum in the following concentrations: from 50 to weight percent beryllium; from 0.5 to 40 weight percent copper; and from 0.5 to 30 weight percent'aluminum; and the combined weight of beryllium, copper, and aluminum being at least 81 percent of the total weight of the alloy. It being an objectof this invention to provide alloys of light weight, decreasing the beryllium content below about 50 Weight percent and increasing the copper content above about 40 Weight percent would be'antitheti'c to that object. With regard to aluminum, it is heavier than beryllium and is inferior in hardness and strength whereby, for the purposes of this invention the above indicated upper limit for aluminum content should not be exceeded.

Silicon forms alloys with copper and with aluminum at and below the melting points of those mixtures of copper and aluminum which fall Within the ranges of copper and aluminum set forth above. When added to such mixtures, silicon increases the Wetting properties of the mixtures in molten phase and thereby enhances diffusion of the ingredients during sintering. Because silicon enhances the wetting and diffusion properties of the ingredients of the alloys of this invention, its presence increases densification and shrinking of the compacts during sintering. If silicon is present in excess of about 5 weight percent, it tends to accumulate and precipitate out from the alloy and to segregate at the boundaries of the primary alloy grains. Silicon oxidizes readily and excess silicon and.(or) its compounds causes brittleness. Preferably, the'silicon content in the alloys of this invention should be kept below about 3 'weight'percent.

Preferred alloys of this invention are those within the following ranges of composition:

Weight, percent Beryllium from 60 to 90 Copper from 9 to 30 Aluminum from 1 to 12 Silicon from to 3 Nickel may be present in the alloys of this invention. Nickel and copper are practically of the same density and are mutually soluble. Nickel being several times heavier than beryllium, its content in the alloys of this invention should not exceed about 12 weight percent so as to keep the total weight of the alloy preferably below that of an equal volume of aluminum. The presence of nickel reduces the tendency of the molten matrix of copper and aluminum to bleed from the beryllium powder during sintering of the beryllium-copper-aluminum compact.

Manganese and magnesium in amounts up to about 1 weight percent may be present in the alloys of this invention without adversely affecting the desired properties of such alloys. Manganese, though generally advantageous as an alloy additive for various alloys, oxidizes readily and therefore if present above about 1 weight percent tends to impair densification of a compact being sintered according to this invention. Magnesium, though of low density, volatilizes readily at elevated temperatures whereby when present in a concentration above about 1 weight percent is a cause of pores in a sintered mass. Some of the impurities commonly found in raw materials or picked up during process are Fe, Na, Ca, Ba, Ti, N, B, C, O, and carbides and oxides. These, too, should not be present in concentrations greater than about 1 weight percent.

Inasmuch as it is within the scope of this invention that manganese, magnesium, and other common inpurities may be present in the alloys of this invention to the extent indicated above without materially affecting the density, strength and melting point of the new alloys, and that nickel and silicon may be present in the amounts of up to about 12 weight percent and 5 weight percent, respectively, a practical minimum limit for the total content of beryllium, copper and aluminum as essential ingredients is about 81 weight percent.

The preparation of sintered alloys of this invention is hereinafter illustrated by description in connection with the following examples:

Example 1 The following ingredients in powder form were intimately mixed for one-half hour in a ceramic ball mill: 70 grams of beryllium; 19.6 grams of copper; 8.4 grams of aluminum; and 2 grams of silicon. The copper, aluminum, and silicon powders were of a size which passed through a 100 mesh screen while the beryllium powder was of a size which passed through a 200 mesh screen. The copper, aluminum, and silicon were at least 99 percent pure while the beryllium powder had a chemical analysis as is set forth in the following table:

TABLE I Chemical Symbol Amount Chemical Symbol Amount Be, wt. percent 98. 6 N, BcO, wt. percent--." 1.6 B, pp. 20-100 0 (as Be C), wt. pcrcc 0.1 Zr, p.p.m 100 Fe, p.p m 1, 300 Ba, p.p. 100 Al, p.p.m 400 T1, p.p. 100 Si, p.p.m 280 Sr, p.p. l00 Mg, p.p m- 180 K, p.p. 100 Ni, p.p.m 160 Z11, p.p. 30-50 Cr, p.p m. 140 Sn, p.p. 5 Mn, p.p m 90 Ag, p.p. 4 Cu, p.p n1- -200 Po, p.p. 2 Na, p.p m 50-500 00, pp. 1-2 Ca, p.p m 50-500 Cd, p.p. -1

1 Up to 500 p.p.m.

The mixed powders were loaded into a flat tensile bar die and were compacted with top and bottom pressures of 35 t.s.i. A bar of compacted powders, having a pressed density of approximately percent of its theoretical maximum density, was removed from the die and was placed in a furnace and heated at a temperature of 1150" C. for four hours in a vacuum of less than 10 microns pressure. The bar was allowed to cool to atmospheric temperature and was removed from the furnace for determination of its properties which are set forth in Table II hereinafter.

Examination of the bar under a metallurgical microscope in polarized light revealed that the bar consisted of randomly oriented alloy grains with each being surrounded by an alloy matrix as is represented in the accompanying drawing which is copied from a photomicrograph of a cross section of the bar taken with a magnification of 200 under polarized light.

In the drawing, the closed areas, some of which are designated by reference numerals 10, 11, 12, and 13, respectively, represent primary grains of beryllium-copper alloy determined to be such from electron microprobe analysis. The various primary grains of beryllium-copper are illustrated in the drawing with cross-hatching at different angles respectively, so as to indicate that in the photomicrogram from which the drawing was made the beryllium-copper grains are of various shades of grey. The alloy matrix is represented by horizontal cross-hatching and is designated by reference numeral 15. Examination of the matrix 15 by electron microprobe analysis showed it to be an alloy of copper, aluminum, and silicon.

Examples 2-11 The procedure described in Example 1 was followed generally for Examples 2-11 with exceptions in operating conditions as are mentioned hereinafter. The concentrations of ingredients and the results of tests for Examples 1-11 are set forth in Table II as follows:

TABLE 11 Copper, Alumi- Silicon, sintered Theo- Percent Rockwell- Ultimate Proportional Modulus of Percent Wt. num, Wt. Density retical Densifi- B Tensile Elastic Elasticity 1n Elongation Percent Wt. Percent in g./cc. Density cation Hardness Strength Llmlt in mlllion p.s.1. in One Percent in gJcc. in 1,000 p.s.1. 1,000 p.s.1. Inch 19. 6 8. 4 2 2. 20 2. 27 97.0 87 43. 2 38. 5 41.0 2. 1 1. 7 26. 3 2 1. 97 2.06 95. 7 39 22. 4 15.0 41.9 4. 2 84 18. 6 1 1. 95 1. 95 100.0 42 25.8 12.0 16.8 3.0 36. 8 3. 2 1 2. 01 2. 66 98. 2 98 19. 4 17. 2 46. 1 2. 5 l 16. 8 1 2.10 2. 18 96. 3 41.0 36. 9 22. 6 1. 7 16 2.00 2. 18 95. 3 75-81 18. 7 11/11 35. 6 1.0 16 2. 12 2. 19 97. 1 83-85 40. 6 19.6 44. 2 1.0 9 1. 94 2.00 97. 2 84-85 42. 8 n/d n/d n/d 8 1. 91 1. 99 95. 8 79-84 40. 8 n/(l n/d n/d 7 1. 93 1.98 97. 5 -83 39. 7 n/d n/d n/d 3 1. 1. 94 97.9 72-73 35. 3 n/d n/d n/d In Table II, the symbol n/ d means not determined.

Example 3 contained 0.16 weight percent manganese and 0.1 weight percent magnesium. Example 5 contained 11.2 weight percent nickel.

The operating conditions for Examples 2-11 varied from those for Example 1 in the following respects: Compacting pressures of from 15 t.s.i. to 40 t.s.i. were employed. Sintering temperatures ranged from 1100 C.- 1150 C. Sintering times ranged from /2 to 4 hours. All examples were sintered in an inert environment, some in a vacuum of less than 500 microns and others in an inert atmosphere of argon for example. For some examples, the beryllium powder was of a size passing through a 100 mesh screen. Some examples were compacted with hydrostatic pressing to a sphere.

In all examples, densification occurred to an extent of at least 95 percent of theoretical density. It is to be noted, too, that all of the sintered alloys of the examples are substantially lighter in weight than an equal volume of aluminum. Also, Table II shows that variations in composition provide wide ranges of properties. In the case of Example 5, for instance, with a significant nickel content it exhibits a relatively high tensile strength but relatively low modulus. Example 3, containing manganese and magnesium, had a relatively low modulus and high ductility. Example 4 had a higher modulus and a lower tensile strength than Example 1. The mechanical properties listed in Table II are as-sintered properties. Working of the alloys as by extrusion and rolling, for example, will change the values of the properties.

According to this invention, the alloys may be formed by hot pressing or they may be formed by slip casting and sintering, or they may be produced by extrusion, either hot or cold, followed by sintering. The alloys of this invention may be densified by infiltration techniques, i.e. pressing beryllium powder to desired density and allowing a molten mixture of ingredients other than beryllium to drain into the porous compact of beryllium. Temperatures of from 1050 C. to 1200 C. may be employed for sintering the alloys of this invention.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

Having described the invention, what is claimed is:

1. The method of forming a substantially isotropic sintered alloy mass consisting essentially of the following ingredients:

from 50 to 90 weight percent beryllium,

from 0.5 to 40 weight percent copper,

from 0.5 to 30 weight percent aluminum,

from to 5 weight percent silicon,

from 0 to 12 weight percent nickel,

from 0 to 1 weight percent manganese, and,

from 0 to 1 weight percent magnesium; the method comprising the steps of compacting a mixture of said ingredients in powder form and of a size passing through a 100 mesh screen, heating the compacted mixture in an inert environment at a temperature above the melting point of aluminum and below the melting point of beryllium for a time sufficient to density the mixture to at least 95 percent of its theoretical density, with the ingredients other than beryllium forming a molten matrix between the beryllium particles, and thereafter cooling the densitied mixture to atmospheric temperature, whereby said copper and beryllium form primary grains which assume random orientation in said mass.

2. The method of claim 1 in which the compacting and heating steps are performed successively.

3. The method of claim 1 in which the compacted mixture is heated at a temperature of from 1050 C. to 1200 C.

4. The method of claim 1 in which the heating time is from /2 to 4 hours.

5. The method of claim 1 in which said inert environment is a vacuum of less than about 500 microns pressure.

6. The method of claim 1 in which said inert environment is an inert atmosphere.

7. The method of claim 6 in which said inert atmosphere is argon.

8. The method of forming a substantially isotropic sintered alloy mass having a high modulus to weight ratio and consisting essentially of the following ingredients:

from to weight percent beryllium,

from 9 to 30 weight percent copper,

from 1 to 12 weight percent aluminum, and

from 0 to 3 weight percent silicon; the method comprising the steps of compacting a mixture of said ingredients in powder form and of a size passing through a 100 mesh screen, heating the compacted mixture in an inert environment at a temperature above the melting point of aluminum and below the melting point of beryllium for a time sufficient to density the mixture to at least percent of its theoretical density, with the ingredients other than beryllium forming a molten matrix between the beryllium particles, and thereafter cooling the densified mixture to atmospheric temperature, whereby said copper and beryllium form primary grains which assume random orientation in said mass.

References Cited UNITED STATES PATENTS 3,196,007 7/1965 Wikle 24182.XR

3,325,257 6/1967 Ang 24-182 L. DEWAY NE RUTLEDGE, Primary Examiner.

A' J. STEINER, Assistant Examiner. 

1. THE METHOD OF FORMING A SUBSTANTIALLY ISOTROPIC SINTERED ALLOY MASS CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS: FROM 50 TO 90 WEIGHT PERCENT BERYLLIUM, FROM 0.5 TO 40 WEIGHT PERCENT COPPER, FROM 0.5 TO 30 WEIGHT PERCENT ALUMINUM, FROM 0 TO 5 WEIGHT PERCENT SILICON, FROM 0 TO 12 WEIGHT PERCENT NICKEL, FROM 0 TO 1 WEIGHT PERCENT MANGANESE, AND, FROM 0 TO 1 WEIGHT PERCENT MAGNESIUM; THE METHOD COMPRISING THE STEPS OF COMPACTING A MIXTURE OF SAID INGREDIENTS IN POWDER FORM AND OF A SIZE PASSING THROUGH A 100 MESH SCREEN, HEATING THE COMPACTED MIXTURE IN AN INERT ENVIRONMENT AT A TEMPERATURE ABOVE THE MELTING POINT OF ALUMINUM AND BELOW THE MELTING POINT OF BERYLLIUM FOR A TIME SUFFICIENT TO DENSIFY THE MIXTURE TO AT LEAST 95 PERCENT OF ITS THEORETICAL DENSITY, WITH THE INGREDIENTS OTHER THAN BERYLLIUM FORMING A MOLTEN MATRIX BETWEEN THE BERYLLIUM PARTICLES, AND THEREAFTER COOLING THE DENSIFIED MIXTURE TO ATMOSPHERIC TEMPERATURE, WHEREBY SAID COPPER AND BERYLLIUM FORM PRIMARY GRAINS WHICH BY SAID COPPER AND BERYLLIUM FORM PRIMARY GRAINS WHICH ASSUME RANDOM ORIENTATION IN SAID MASS. 